[PATCH v8 6/7] drm: avoid circular locks in drm_lease_held

Desmond Cheong Zhi Xi desmondcheongzx at gmail.com
Thu Aug 26 02:01:21 UTC 2021


drm_lease_held calls drm_file_get_master. However, this function is
sometimes called while holding on to drm_device.master_rwsem or
modeset_mutex. Since master_rwsem will replace
drm_file.master_lookup_lock in drm_file_get_master in a future patch,
this results in both recursive locking, and an inversion of the
master_rwsem --> modeset_mutex lock hierarchy.

To fix this, we create a new drm_lease_held_master helper function
that enables us to avoid calling drm_file_get_master after locking
master_rwsem or modeset_mutex.

Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx at gmail.com>
---
 drivers/gpu/drm/drm_auth.c    |  3 +++
 drivers/gpu/drm/drm_crtc.c    |  4 +++-
 drivers/gpu/drm/drm_encoder.c |  7 ++++++-
 drivers/gpu/drm/drm_lease.c   | 30 +++++++++++++++---------------
 drivers/gpu/drm/drm_plane.c   | 18 ++++++++++++++----
 include/drm/drm_lease.h       |  2 ++
 6 files changed, 43 insertions(+), 21 deletions(-)

diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c
index 65065f7e1499..f2b2f197052a 100644
--- a/drivers/gpu/drm/drm_auth.c
+++ b/drivers/gpu/drm/drm_auth.c
@@ -410,6 +410,9 @@ struct drm_master *drm_file_get_master(struct drm_file *file_priv)
 {
 	struct drm_master *master = NULL;
 
+	if (!file_priv)
+		return NULL;
+
 	spin_lock(&file_priv->master_lookup_lock);
 	if (!file_priv->master)
 		goto unlock;
diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index b1279bb3fa61..0b1e76d2f9ff 100644
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -665,8 +665,10 @@ int drm_mode_setcrtc(struct drm_device *dev, void *data,
 
 	plane = crtc->primary;
 
+	lockdep_assert_held_once(&dev->master_rwsem);
 	/* allow disabling with the primary plane leased */
-	if (crtc_req->mode_valid && !drm_lease_held(file_priv, plane->base.id))
+	if (crtc_req->mode_valid &&
+	    !drm_lease_held_master(file_priv->master, plane->base.id))
 		return -EACCES;
 
 	DRM_MODESET_LOCK_ALL_BEGIN(dev, ctx,
diff --git a/drivers/gpu/drm/drm_encoder.c b/drivers/gpu/drm/drm_encoder.c
index 72e982323a5e..bacb2f6a325c 100644
--- a/drivers/gpu/drm/drm_encoder.c
+++ b/drivers/gpu/drm/drm_encoder.c
@@ -22,6 +22,7 @@
 
 #include <linux/export.h>
 
+#include <drm/drm_auth.h>
 #include <drm/drm_bridge.h>
 #include <drm/drm_device.h>
 #include <drm/drm_drv.h>
@@ -281,6 +282,7 @@ int drm_mode_getencoder(struct drm_device *dev, void *data,
 	struct drm_mode_get_encoder *enc_resp = data;
 	struct drm_encoder *encoder;
 	struct drm_crtc *crtc;
+	struct drm_master *master;
 
 	if (!drm_core_check_feature(dev, DRIVER_MODESET))
 		return -EOPNOTSUPP;
@@ -289,13 +291,16 @@ int drm_mode_getencoder(struct drm_device *dev, void *data,
 	if (!encoder)
 		return -ENOENT;
 
+	master = drm_file_get_master(file_priv);
 	drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
 	crtc = drm_encoder_get_crtc(encoder);
-	if (crtc && drm_lease_held(file_priv, crtc->base.id))
+	if (crtc && drm_lease_held_master(master, crtc->base.id))
 		enc_resp->crtc_id = crtc->base.id;
 	else
 		enc_resp->crtc_id = 0;
 	drm_modeset_unlock(&dev->mode_config.connection_mutex);
+	if (master)
+		drm_master_put(&master);
 
 	enc_resp->encoder_type = encoder->encoder_type;
 	enc_resp->encoder_id = encoder->base.id;
diff --git a/drivers/gpu/drm/drm_lease.c b/drivers/gpu/drm/drm_lease.c
index 1b156c85d1c8..15bf3a3c76d1 100644
--- a/drivers/gpu/drm/drm_lease.c
+++ b/drivers/gpu/drm/drm_lease.c
@@ -114,27 +114,30 @@ bool _drm_lease_held(struct drm_file *file_priv, int id)
 	return _drm_lease_held_master(file_priv->master, id);
 }
 
-bool drm_lease_held(struct drm_file *file_priv, int id)
+bool drm_lease_held_master(struct drm_master *master, int id)
 {
-	struct drm_master *master;
 	bool ret;
 
-	if (!file_priv)
+	if (!master || !master->lessor)
 		return true;
 
-	master = drm_file_get_master(file_priv);
-	if (!master)
-		return true;
-	if (!master->lessor) {
-		ret = true;
-		goto out;
-	}
 	mutex_lock(&master->dev->mode_config.idr_mutex);
 	ret = _drm_lease_held_master(master, id);
 	mutex_unlock(&master->dev->mode_config.idr_mutex);
 
-out:
-	drm_master_put(&master);
+	return ret;
+}
+
+bool drm_lease_held(struct drm_file *file_priv, int id)
+{
+	struct drm_master *master;
+	bool ret;
+
+	master = drm_file_get_master(file_priv);
+	ret = drm_lease_held_master(master, id);
+	if (master)
+		drm_master_put(&master);
+
 	return ret;
 }
 
@@ -150,9 +153,6 @@ uint32_t drm_lease_filter_crtcs(struct drm_file *file_priv, uint32_t crtcs_in)
 	int count_in, count_out;
 	uint32_t crtcs_out = 0;
 
-	if (!file_priv)
-		return crtcs_in;
-
 	master = drm_file_get_master(file_priv);
 	if (!master)
 		return crtcs_in;
diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
index b5566167a798..907b026fd916 100644
--- a/drivers/gpu/drm/drm_plane.c
+++ b/drivers/gpu/drm/drm_plane.c
@@ -23,6 +23,7 @@
 #include <linux/slab.h>
 #include <linux/uaccess.h>
 
+#include <drm/drm_auth.h>
 #include <drm/drm_plane.h>
 #include <drm/drm_drv.h>
 #include <drm/drm_print.h>
@@ -687,6 +688,7 @@ int drm_mode_getplane(struct drm_device *dev, void *data,
 	struct drm_mode_get_plane *plane_resp = data;
 	struct drm_plane *plane;
 	uint32_t __user *format_ptr;
+	struct drm_master *master;
 
 	if (!drm_core_check_feature(dev, DRIVER_MODESET))
 		return -EOPNOTSUPP;
@@ -695,10 +697,13 @@ int drm_mode_getplane(struct drm_device *dev, void *data,
 	if (!plane)
 		return -ENOENT;
 
+	master = drm_file_get_master(file_priv);
 	drm_modeset_lock(&plane->mutex, NULL);
-	if (plane->state && plane->state->crtc && drm_lease_held(file_priv, plane->state->crtc->base.id))
+	if (plane->state && plane->state->crtc &&
+	    drm_lease_held_master(master, plane->state->crtc->base.id))
 		plane_resp->crtc_id = plane->state->crtc->base.id;
-	else if (!plane->state && plane->crtc && drm_lease_held(file_priv, plane->crtc->base.id))
+	else if (!plane->state && plane->crtc &&
+		 drm_lease_held_master(master, plane->crtc->base.id))
 		plane_resp->crtc_id = plane->crtc->base.id;
 	else
 		plane_resp->crtc_id = 0;
@@ -710,6 +715,8 @@ int drm_mode_getplane(struct drm_device *dev, void *data,
 	else
 		plane_resp->fb_id = 0;
 	drm_modeset_unlock(&plane->mutex);
+	if (master)
+		drm_master_put(&master);
 
 	plane_resp->plane_id = plane->base.id;
 	plane_resp->possible_crtcs = drm_lease_filter_crtcs(file_priv,
@@ -1114,6 +1121,7 @@ static int drm_mode_cursor_common(struct drm_device *dev,
 		return -ENOENT;
 	}
 
+	lockdep_assert_held_once(&dev->master_rwsem);
 	drm_modeset_acquire_init(&ctx, DRM_MODESET_ACQUIRE_INTERRUPTIBLE);
 retry:
 	ret = drm_modeset_lock(&crtc->mutex, &ctx);
@@ -1128,7 +1136,8 @@ static int drm_mode_cursor_common(struct drm_device *dev,
 		if (ret)
 			goto out;
 
-		if (!drm_lease_held(file_priv, crtc->cursor->base.id)) {
+		if (!drm_lease_held_master(file_priv->master,
+					   crtc->cursor->base.id)) {
 			ret = -EACCES;
 			goto out;
 		}
@@ -1235,7 +1244,8 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
 
 	plane = crtc->primary;
 
-	if (!drm_lease_held(file_priv, plane->base.id))
+	lockdep_assert_held_once(&dev->master_rwsem);
+	if (!drm_lease_held_master(file_priv->master, plane->base.id))
 		return -EACCES;
 
 	if (crtc->funcs->page_flip_target) {
diff --git a/include/drm/drm_lease.h b/include/drm/drm_lease.h
index 5c9ef6a2aeae..426ea86d3c6a 100644
--- a/include/drm/drm_lease.h
+++ b/include/drm/drm_lease.h
@@ -18,6 +18,8 @@ bool drm_lease_held(struct drm_file *file_priv, int id);
 
 bool _drm_lease_held(struct drm_file *file_priv, int id);
 
+bool drm_lease_held_master(struct drm_master *master, int id);
+
 void drm_lease_revoke(struct drm_master *master);
 
 uint32_t drm_lease_filter_crtcs(struct drm_file *file_priv, uint32_t crtcs);
-- 
2.25.1



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